We wash, clean of scales and blood, and dry the tuna. In a saucepan with a little olive oil we mark a few seconds on each sideremove to a plate, remove the bones and skin, salt and reserve.
In the same pan, add a little more oil if necessary, poach the chopped onion, pepper and garlic together with the chilli. Add the tomato sauce, enough to cover the tuna and let the mixture cook for 20 minutes. We remove the chilli, pass the sauce through the food mill and return it to the pot.
We throw the nice and let it cook for a minute over low heat. Remove the pan from the heat, let it rest for a couple of minutes and serve immediately so that the bonito does not dry out.